Method for producing a film of an aromatic amide oxadiazole polymer containing an oxadiazole structure and the film so produced

ABSTRACT

A compound having an oxadiazole structure which is obtained by dehydration-cyclization of a compound having a carbohydrazide structure using a chemical agent selected from acids and bases. The dehydration-cyclization of the compound having a carbohydrazide structure can be conducted under mild conditions at low cost.

This application is a division of application Ser. No. 12/382,491, filedMar. 17, 2009, which is a division of Ser. No. 10/547,526, filed Sep. 2,2005 (now U.S. Pat. No. 7,511,112), which is a 371 of internationalapplication PCT/JP2004/002535, filed Mar. 2, 2004, which claims prioritybased on Japanese Patent Application No. 2003-058181, filed Mar. 5,2003, each of which is incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to highly heat-resistant, highly rigidaromatic polymers and to films, new chemical reactions of carbohydrazidecompounds, electrolyte membranes and fuel cells using the polymers.

BACKGROUND ART

As highly heat-resistant, highly rigid polymers, aromatic polyamides areknown. The aromatic polyamides are polymers useful as engineeringmaterials due to their high heat resistance and high mechanicalstrength. In particular, aromatic polyamides composed of para-directedaromatic groups represented by polyparaphenylene terephthalamide(hereinafter, referred to as PPTA) are of great utility value becausethey can result in shaped articles superior in strength and elasticmodulus as well as the aforementioned properties due to their highstiffness. A para-directed aromatic polyamide typified by PPTA, however,exhibits low solubilities in solvents and dissolves only in extremelyrestricted solvents such as sulfuric acid. There, therefore, aresignificant limitations in process. A solution thereof causes no seriousproblems when fibers are produced therefrom. When it is processed into ashaped article of two or more dimensions such as film, however, it mustbe processed by a special shaping technique because the solutionexhibits an optical anisotropy. Therefore, improvement is required inthis respect.

On the other hand, as an approach to improve solubility, introduction ofstructural units having a bridge such as oxygen or a methylene group isknown in U.S. Pat. No. 4,075,172 and Japanese Patent ApplicationPublication No. 52-98795. Generally, however, the introduction of suchstructural units will affect superior mechanical characteristics, suchas Young's modulus and strength, inherent to para-directed aromaticpolyamides. As another approach, aromatic polyamides having an aromaticnucleus with a chlorine atom introduced thereto has been proposed inJapanese Patent Application Publication Nos. 52-84246 and 54-106564. Themonomers of such aromatic polyamides, however, are expensive and thosepolymers are not conformable to a current trend that halogen-containingpolymers are not preferred.

As a highly heat-resistant, highly rigid polymer other than aromaticpolyamides, an aromatic carbohydrazide is disclosed in Japanese PatentNo. 2853117, which discloses that a film which can exhibit an extremelyhigh Young's modulus even in one direction is obtained by stretching.This film, however, has a high moisture absorption inherently due to itspolymer structure.

Moreover, U.S. Pat. No. 3,642,711 discloses a method for obtaining ahighly heat-resistant polymer through thermal dehydration-cyclization ofan aromatic carbohydrazide. This method is, however, disadvantageous inindustrial aspect because the cyclization reaction needs temperatures ashigh as 350° C. under reduced pressure. In addition, a thermalcyclization reaction is problematic in that if the reaction time isshort, the cyclization reaction will proceed insufficiently, whereas ifthe reaction time is long, side reactions such as a decompositionreaction will take place.

As an electrolyte membrane, Nafion (registered trademark) of E. I. duPont de Nemours and Company is used widely. This is problematic in thatthe cost is very high and the heat-resisting temperature is low becauseof the use of fluororesin in the polymer. Hydrocarbon-based electrolytemembranes are problematic in that they are of low mechanical strengththough they are advantageous is cost. Thus, inexpensive electrolytemembranes having a high heat-resisting temperature and a high mechanicalstrength are demanded.

DISCLOSURE OF THE INVENTION

The present invention was accomplished through a study for overcomingthe problems with the above-mentioned prior art. That is to say, anobject of the present invention is to obtain an aromatic polymer whichis soluble in an aprotic polar solvent and which exhibits a high Young'smodulus, a great elongation at break and a low moisture absorption whenbeing formed into a film. Another object of the present invention is tocause a carbohydrazide structure to undergo dehydration-cyclizationunder mild conditions at low cost. Still another object of the presentinvention is to obtain an electrolyte membrane having a highheat-resisting temperature and a high rigidity at low cost.

The present invention is characterized by an aromatic polymer comprisingstructural units represented by chemical formulas (I), (II) and (III)shown below and satisfying formulas (1) to (3) shown below when molarfractions (%) of the structural units of the chemical formulas (I), (II)and (III) are represented by l, m and n, respectively:

80≦l+m+n≦100   (1)

5≦m≦90   (2)

10≦n≦90   (3)

R¹: an aromatic group

R²: an aromatic group

R³: an aromatic group having 12 or more carbon atoms which has at leastone substituent selected from the group consisting of ether (—O—),methylene (—CH₂—) and sulfone (—SO₂—)

R⁴: an aromatic group

R⁵: an aromatic group

R⁶: an aromatic group.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing the structure of a fuel cell.

BEST MODE FOR CARRYING OUT THE INVENTION

The aromatic polymer of the present invention can exhibit solubility insolvent, a high rigidity and a high heat resistance simultaneously bycontaining aromatic polyamide structures represented by chemicalformulas (I) and (II) shown below and an aromatic carbohydrazidestructure represented by chemical formula (III) shown below.

R¹: an aromatic group

R²: an aromatic group

R³: an aromatic group having 12 or more carbon atoms which has at leastone substituent selected from the group consisting of ether (—O—),methylene (—CH₂—) and sulfone (—SO₂—)

R⁴: an aromatic group

R⁵: an aromatic group

R⁶: an aromatic group.

As R¹ to R⁶ in the chemical formulas shown above, any aromatic groupsmay be used. Aromatic groups containing no halogen atoms are preferredas R¹ to R⁶ because they are conformable to a current trend thathalogen-containing polymers are not preferred. Moreover, they arepreferably structural units represented by chemical formula (V) shownbelow for attaining one of the objects of the present invention, namely,to obtain an aromatic polymer which is soluble in an aprotic polarsolvent and which exhibits a high Young's modulus and a low moistureabsorption when being formed into film.

As X, a hydrogen atom, halogen atoms and organic groups having 1 to 4carbon atoms but containing no halogen atoms are preferably used. Morepreferred are a methyl group, an ethyl group, a propyl group, a butylgroup and a cyano group. In the molecule, a plurality of kinds ofsubstituents may coexist.

R¹ is an aromatic group containing no substituent selected from thegroup consisting of an ether group (—O—), a methylene group (—CH₂—) or asulfone group (—SO₂—). These substituents are necessary for structuralunits represented by chemical formula (II). These substituents, however,impart flexibility to polymers. The Young's modulus, therefore, may beless than 5 GPa if not only structural units represented by chemicalformula (II) but also structural units represented by chemical formula(I) have these flexible substituents. It is more desirable that R¹ be agroup selected from a phenyl group, a biphenyl group, a terphenyl group,a naphthalene group, an anthracene group, a diaminobenzanilide residueand a 9,9-bis(4-aminophenyl)fluorene residue. It should be noted thatpart or all of the hydrogen of an aromatic ring may be substituted withanother or other atoms or substituents. In addition, aromatic groupscontaining no halogen atoms are preferred as R¹ because they areconformable to a current trend that halogen-containing polymers are notpreferred.

As R², a para-directed phenylene group is preferred, provided that eachof the hydrogen atoms at 2-, 3-, 5- and 6-positions of the aromatic ringmay be substituted with another atom or substituent.

R³ is an aromatic group having 12 or more carbon atoms which has atleast one substituent selected from the group consisting of an ethergroup (—O—), a methylene group (—CH₂—) and a sulfone group (—SO₂—).Preferred are aromatic groups including 12 or more but not more than 100carbon atoms having a structure in which two aromatic groups selectedindependently from a phenyl group, a biphenyl group, a terphenyl group,a naphthalene group, an anthracene group, a diaminobenzanilide residueand a 9,9-bis(4-aminophenyl)fluorene residue, provided that part or allof the hydrogen thereof may be substituted with other group(s), arecombined through at least one substituent selected from the groupconsisting of an ether group (—O—), a methylene group (—CH₂—) and asulfone group (—SO₂—). R³ is more desirably an aromatic group in whichphenyl groups are combined through at least one substituent selectedfrom the group consisting of an ether group (—O—), a methylene group(—CH₂—) and a sulfone group (—SO₂—). It should be noted that part or allof the hydrogen of an aromatic ring may be substituted with another orother atoms or substituents.

As R³, bisphenoxybenzene groups are more desirable and a1,3-bis(4-phenoxy)benzene group, which is represented by chemicalformula (IV), is the most desirable.

As R⁴, a para-directed phenylene group is preferred, provided that eachof the hydrogen atoms at 2-, 3-, 5- and 6-positions of the aromatic ringmay be substituted with another atom or substituent.

As R⁵, a group selected from a phenyl group, a biphenyl group and anaphthalene group is desirable and a 2,6-naphthalene group is moredesirable. It should be noted that each of the hydrogen atoms of thearomatic rings may be substituted with another atom or substituent.

As R⁶, a para-directed phenylene group is preferred, provided that eachof the hydrogen atoms at 2-, 3-, 5- and 6-positions of the aromatic ringmay be substituted with another atom or substituent.

The elements or substituents with which hydrogen of the aromatic ringsin R¹ to R⁶ are substituted may be, but are not particularly restrictedto, halogens, inorganic groups, organic groups, organometallic groups,etc. These substituents contribute to impartation of functions, but theycontribute less to heat resistance and mechanical properties becausethey are substituents on side chains. The following are examples ofcombinations of a function imparted and a substituent. Substitution witha halogen atom can reduce the moisture absorption of the aromaticpolymer. Substitution with an acidic group such as sulfonic acid andphosphonic acid can improve the ionic conductance of the aromaticpolymer. Substitution with a bulky group can improve the solubility ofthe aromatic polymer. Bonding a reactive group or reactive oligomer suchas a silyl coupling agent, an epoxy group and a thermally curingpolyimide to a side chain can improve the adhesive property of thearomatic polymer. Bonding a fullerene to a side chain can improve thelubricity and electrical characteristics of the aromatic polymer.

Moreover, the aromatic polymer (amide carbohydrazide) of the presentinvention satisfies formulas (1) to (3) shown below when molar fractions(%) of the structural units of the chemical formulas (I), (II) and (III)are represented by l, m and n, respectively:

80≦l+m+n≦100   (1)

5≦m≦90   (2)

10≦n≦90   (3)

When the molar fraction l+m+m (%) of the highly rigid, highlyheat-resistant structural units represented by chemical formulas (I),(II) and (III) is adjusted to 80≦l+m+n≦100, the aromatic polymer of thepresent invention exhibits high rigidity and high heat resistance. Thel+m+m is more preferably 90 to 100%, and even more preferably 95 to100%. If the l+m+n is less than 80%, Young's modulus may become lessthan 5 GPa.

In the aromatic polymer of the present invention, the molar fraction 1(%) of the aromatic polyamide structural unit represented by chemicalformula (I) is 0≦l≦75, and more preferably 0≦l≦40. In addition, it ispreferable that 20≦l+n≦95. Among the structural units represented bychemical formulas (I), (II) and (III), chemical formulas (I) and (III)are particularly rigid components. When the combined amount of thesecomponents is less than 20 mole%, the Young's modulus may become lessthan 5 GPa, whereas when it exceeds 95 mole %, resulting films may bebrittle and easy to be broken. If n is within an appropriate range, 1may be 0.

In the aromatic polymer of the present invention, the molar fraction m(%) of the aromatic polyamide structural units represented by chemicalformula (II) is 5≦m≦90. When m is less than 5%, the moisture absorptionmay become too high. When m is over 90%, the Young's modulus may becomeless than 5 GPa. The molar fraction m (%) is desirably 10≦m≦80, moredesirably 20≦m≦70.

In the aromatic polymer of the present invention, the molar fraction n(%) of the aromatic dicarbohydrazide structural units represented bychemical formula (III) is 10≦n≦90. Because a hydrazide group representedby —NH—NH— contributes to increase in moisture absorption, the moistureabsorption of a resulting film may become too high when n is greaterthan 90%. Because an aromatic dicarbohydrazide which is a sourcematerial of the structure represented by chemical formula (III),naphthalene dicarbohydrazide, for example, is almost insoluble inorganic solvent, it reacts in the solid state and dissolves only afterchanging into a polymer. Therefore, if n is greater than 90%, thereaction will proceed very slowly and it may become difficult to obtainpolymers with high molecular weights. On the other hand, if n is lessthan 10%, a resulting film may have a low rigidity. n is desirably20≦n≦90, more desirably 30≦n≦70, and most desirably 40≦n≦60.

It is also desirable that part or all of the aromatic carbohydrazidestructures represented by chemical formula (III) be cyclized bydehydration as shown in chemical formula (VII) to be converted to apolyoxazole structure. In other words, the aromatic polymer of thepresent invention includes aromatic amide carbohydrazide polymerscontaining a carbohydrazide structure, aromatic amide oxadiazolepolymers containing an oxadiazole structure resulting fromdehydration-cyclization of a carbohydrazide structure, and composites ofboth types of polymers. When part or all of the carbohydrazidestructures are changed into polyoxazole structures, the Young's modulusof the aromatic polymer will be improved greatly.

R⁵: an aromatic group

R⁶: an aromatic group.

As a method for dehydration-cyclizing aromatic carbohydrazide structuresto form oxadiazole rings, thermal methods are widely known. The thermalmethods, however, need a high temperature of 350° C. under reducedpressure. Through extensive studies, the present inventors found a newchemical reaction to convert a compound having a carbohydrazidestructure to a compound having an oxadiazole structure by causing thecompound having a carbohydrazide structure to react by means of achemical agent. This method is favorable due to its industrialadvantages because it is possible, according to this method, to producecompounds having an oxadiazole structure at room temperature undernormal pressure.

As the chemical agent to be used for the dehydration-cyclization, achemical agent selected from acids and bases. The acids used hereininclude acid anhydrides. As the acids, fatty acid anhydrides such asacetic anhydride and aromatic acid anhydrides, for example, aredesirably employed. As the bases, organic bases, inorganic bases and thelike are desirably employed. Specific examples of the organic basesinclude aliphatic amines such as triethylamine, aromatic tertiary aminessuch as dimethylaniline, heterocyclic tertiary amines such as pyridine,picoline and isoquinoline, ammonia and hydrazides. Particularly,nitrogen-containing compounds having 0 to 10 carbon atoms are desirablyused due to their superior safety. As the nitrogen-containing compoundshaving 0 to 10 carbon atoms, aliphatic amines having 1 to 3 carbon atomssuch as triethylamine and ethanolamine are particularly desirable, anddiethanolamine or triethanolamine is the most desirable. Regarding thechemical agent to be used for the dehydration-cyclization, it ispermissive to use a single kind of chemical agent, a combination of aplurality of chemical agents, or a chemical agent or chemical agentsdiluted in solvent. Because it is possible to carry outdehydration-cyclization at a high efficiency by means of a safe chemicalagent such as diethanolamine, and triethanolamine without usingdangerous dehydrating agents such as concentrated sulfuric acid with noneed for high temperature or reduced pressure, the present invention canprovide a production method extremely advantageous in the industrialaspect. No simple and easy method for synthesizing a compound having anoxadiazole ring has heretofore been known. The present inventionprovides a novel and useful method for producing a compound having anoxadiazole ring.

The “chemical reaction” used herein means the change of a carbohydrazidestructure to another structure. The chemical agent to be used for thedehydration-cyclization may be a catalyst, which does not change beforeand after the reaction. When a base such as amine is used, it probablyacts as a catalyst to cause a dehydration-cyclization reaction. When anacid anhydride is used, a dehydration-cyclization reaction is probablycaused by the dehydrating action of the acid anhydride. An acidanhydride and a base may be used in the form of a mixture thereof ifthey are a combination of substances which do not react to each other,such as acetic anhydride and pyridine.

Whether the compound containing a carbohydrazide structure is a highmolecular weight compound or a low molecular weight compound, it can beconverted to an oxadiazole structure through that reaction. When thecompound containing a carbohydrazide structure is an aromatic polymer, aresulting polymer containing an oxadiazole structure is very useful asan aromatic polymer possessing a high heat resistance and a highrigidity. In addition to this, compounds having an oxadiazole structureare useful also as, for example, organic EL material, organic conductivematerial and organic semiconductor.

The method of dehydration-cyclization using a chemical agent is notparticularly restricted. In the case of high molecular weight compounds,examples of the method include a method in which a polymer solution isexpanded in plane on a support and then is immersed in a chemical agentand a method in which a chemical agent is mixed with a polymer at atemperature low enough so that a dehydration-cyclization reaction doesnot proceed and then the mixture is expanded on a support to undergodehydration-cyclization. When the polymer is expanded in a fibrous form,fibers are formed. The dehydration-cyclization reaction proceeds atnormal temperature and normal pressure, but heat treatment may becarried out mainly for drying of the polymer solution or heat setting.

In the case of low molecular weight compounds, dehydration-cyclizationby means of a chemical agent can be conducted in various methods;examples include a reaction in solution and a method in whichcyclization is carried out simultaneously with vapor deposition by vapordeposition polymerization.

The structure of an aromatic polymer is determined generally by sourcematerials thereof, namely, a diamine and a dicarbohydrazide (hereinaftercollectively referred to as “diamine”) and a dicarboxylic acid chloride.The same holds true for the case where an aromatic polymer of thepresent invention is synthesized from isocyanate or carboxylic acid.When the source materials are unknown, structure analysis is carried outfor an aromatic polyamide composition. As a method for the analysis,mass spectrometric analysis, analysis by the nuclear magnetic resonancemethod, spectral analysis, etc. can be used.

In the present invention, examples of the diamine include p-phenylenediamine, 2-nitro-1,4-phenylenediamine, 2-methyl-1,4-phenylenediamine,m-phenylenediamine, 1,5-diaminonaphthalene, 2,6-diaminonaphthalene,4,4′-diaminodiphenyl ether, 3,4′-diaminodiphenyl ether,4,4′-diaminodiphenylsulfone, 3,3′-diaminodiphenylsulfone,2,2′-ditrifluoromethyl-4,4′-diaminobiphenyl, 3,3′-dimethylbenzidine,4,4′-diaminodiphenylmethane, 4,4′-diaminobenzanilide,9,9-bis(4-aminophenyl)fluorene, bis[4-(4-aminophenoxy)phenyl]sulfone,bis[4-(3-aminophenoxy)phenyl]sulfone,2,2-bis[4-(4-aminophenoxy)phenyl]propane,2,2-bis(4-aminophenyl)hexafluoropropane, 1,3-bis(4-aminophenoxy)benzene,1,4-bis(4-aminophenoxy)benzene, 4,4′-bis(4-aminophenoxy)biphenyl,4,4′-diaminodiphenylsulfone, 3,3′-diaminobenzophenone,3,4′-diaminobenzophenone, 4,4′-diaminobenzophenone,1,3-bis(3-aminophenoxy)benzene,2,2′,5,5′-tetrachloro-4,4′-diaminobiphenyl,2,2′-dichloro-4,4′-diamino-5,5′-dimethoxybiphenyl,3,3′-dimethoxy-4,4′-diaminobiphenyl. 1,3-bis(4-aminophenoxy)benzene isthe most desirable.

In the present invention, the dicarbohydrazide includes 2,6-naphthalenedicarbohydrazide, 1,5-naphthalene carbohydrazide, biphenyldicarbohydrazide, terephthalic acid dicarbohydrazide, isophthalic acidcarbohydrazide, etc. 2,6-Naphthalene dicarbohydrazide is preferablyused.

In the present invention, the dicarboxylic acid chloride includeterephthaloyl dichloride, 2chloro-terephthaloyl dichloride, isophthaloyldichloride, naphthalenedicarbonyl chloride, biphenyldicarbonyl chloride,terphenyldicarbonyl chloride, etc. Terephthaloyl dichloride or2chloro-terephthaloyl dichloride is preferably used.

In the present invention, “highly rigid” means having a great tensilemodulus of elasticity (Young's modulus). When being used as a magneticrecording medium, the,polymer film of the present invention preferablyhas a Young's modulus in at least one direction of 5 GPa or more becausethe film will be resistant to the power applied during its processing orapplication, resulting in good planarity. In addition, when the Young'smodulus in at least one direction is 5 GPa or more, it becomes possibleto reduce the thickness of the film.

When the Young's modulus in all directions is less than 5 GPa,deformation may occur during processing. Although there is no upperlimit with the Young's modulus, if it is greater than 20 GPa, thetoughness of the film may be reduced, resulting in difficulty in filmproduction and processing. The Young's modulus is preferably from 5 to20 GPa, more preferably from 7 to 18 GPa, and even more preferably from10 to 16 GPa.

The ratio of the maximum value (Em) of Young's modulus to the Young'smodulus (Ep) in a direction perpendicular thereto, Em/Ep, is preferablyfrom 1.1 to 3 because the film will exert an improved cutability duringits processing. The ratio is more preferably from 1.2 to 2.5, and evenmore preferably from 1.5 to 2.5. If the Em/Ep is greater than 3, a filmmay be rather susceptible to rupture.

The film of the present invention preferably has a moisture absorptionat 25° C./75 RH % of 7% or less, more preferably 5% or less and evenmore preferably 2% or less because change in humidity causes less changein characteristics during its application and processing. The moistureabsorption referred to herein is measured by a method described below.First, about 0.5 g of film is collected and heated at 120° C. for 3hours for demoisturing. Then, the temperature was lowered to 25° C.while the film was prevented from moisture absorption. The weight afterthe temperature lowering is measured accurately to the order of 0.1 mg,where the weight is represented by W0. Subsequently, it is left to standin an atmosphere at 25° C., 75 RH % for 48 hours. Then, the weight ismeasured, which is represented by W1. The moisture absorption iscalculated by use of the following equation.

Moisture absorption rate (%)=((W1−W0)/W1)×100

The lower the moisture absorption, the better it is. However, apractical lower limit is about 0.03%.

It should be noted that when a film is used as an electrolyte membrane,low moisture absorption is not required. The electrolyte membrane isused rather after being improved in affinity with water by itsmodification with a polar group or by doping with acid.

The elongation at break in at least one direction of the film of thepresent invention preferably is 20% or more in the measurement accordingto JIS-C2318. It is more preferably 20 to 300%, and even more preferably30 to 250% because less rupture occurs in film production andprocessing. The upper limit of the elongation at break is notparticularly limited, but it practically is about 250%.

The dielectric constant at 1 kHz of the film of the present invention ispreferably 4 or less. It is more preferably 3.5 or less, and mostpreferably 2 or less. When the dielectric constant is small, it ispossible to reduce the delay of signals when using the film of thepresent invention as an electronic circuit substrate.

The measurement of the dielectric constant can be carried out by use ofan automatic balance bridge at measurement frequencies: 1 k, 1 M and 10MHz (three levels) at a measurement temperature: room temperature (21°C.). A specimen is applied with a three-terminal electrode to form aspecimen under test. Some examples of the measurement conditions are asfollows:

-   Apparatus: Impedance/Gain-Phase Analyzer 4194A manufactured by    HEWLETT PACKARD-   Jig: 16451B DIELECTRIC TEST FIXTURE-   Electrode: Electrically conductive silver paste coating “DOTITE”    manufactured by Fujikura Kasei Co., Ltd.-   Dimensions: Outer diameter of surface electrode inner circle: 37 mm

Inside diameter of surface electrode outer circle: 39 mm

Outer diameter of rear side (counter) electrode: 50 mm

-   The number of measurements: n=5-   Atmosphere in test chamber: 21±2° C., 60±5% RH-   Calculation formula: A dielectric constant ε and a dielectric loss    tangent tan δ are calculated using the following equation:

ε=(Cx×t)/(ε0×A)

tan δ=Gx/2πf·Cx

wherein Cx: electrostatic capacitance (F) of the object

-   -   t: thickness of the specimen (m)    -   A: effective area of the electrode (m²)    -   c: velocity of light    -   ε0: electric constant 8.854×10⁻¹² (F/m)=(4π)⁻¹×c⁻²×10⁷ (m·sec⁻¹)    -   Gx: conductance (S) of the object    -   f: measurement frequency (ω=2πf) (Hz)

It is desirable for the film of the present invention to exhibit athermal shrinkage in at least one direction of 1% or less when beingheat treated at 200° C. for 30 minutes under substantially no tensionbecause the dimensional change during processing and change is phasecontrast characteristic can be controlled. The thermal shrinkage is morepreferably 0.5% or less, and even more preferably 0.3% or less. Thethermal shrinkage is defined by the following equation.

Thermal shrinkage (%)=((Specimen length before heat treatment−Specimenlength after heat treatment and cooling/(Specimen length before heattreatment))×100

The lower the heat shrinkage, the better it is. However, a practicallower limit is about 0.1%. When the heat shrinkage in at least onedirection measured under the aforementioned conditions is 1% or less, itbecomes possible to form an electric circuit or to solder an electronicpart on the polymer film of the present invention. In addition, the filmis strain-resistant when it is attached to another object and,therefore, less warp will occur.

The film of the present invention preferably has a coefficient ofthermal expansion from 80° C. to 120° C. of 50-0 ppm/° C. Thecoefficient of thermal expansion is measured in a temperature loweringstep following temperature elevation to 150° C. When the initial lengthof a specimen at 25° C., 75 Rh % is represented by L0, the length of thespecimen at a temperature T1 is represented by L1 and the length of thespecimen at a temperature T2 is represented by L2, the coefficient ofthermal expansion from T1 to T2 is determined using the followingequation:

Coefficient of thermal expansion (ppm/° C.)=((L2−L1)/L0)/(T2/T1)×10⁶

The coefficient of thermal expansion is more preferably 30-0 ppm/° C.,and even more preferably 20-0 ppm/° C.

Moreover, the film of the present invention preferably has a coefficientof moisture expansion from 30% Rh to 80% Rh at 25° C. of 50-0 ppm/% Rh.In the determination of the coefficient of moisture expansion, a filmwhich will become a sample is first fixed in a high-temperaturehigh-humidity bath so as to have a width of 1 cm and a sample length of15 cm. Moisture is removed to a certain humidity (about 30% Rh). Afterthe film length becomes constant, moisture is added (to about 80% Rh)and the sample thereby begins to lengthen. About 24 hours later, themoisture uptake reaches equilibrium and the elongation of the film alsoreaches equilibrium. Based on the amount of the elongation, thecoefficient is calculated using the following equation.

Coefficient of moisture expansion ((cm/cm)/% Rh)=Amount ofelongation/(Sample length×Humidity difference)

The coefficient of moisture expansion is more preferably 30-0 ppm/% Rh,and even more preferably 20-0 ppm/% Rh. When the coefficient of thermalexpansion and the coefficient of moisture expansion are small, thedimensional change caused by the environment become small and lesserrors will occur when the film is fabricated into a magnetic recordingmaterial.

Examples of the method for producing the aromatic polymer of the presentinvention and the method for producing a film by processing the aromaticpolymer are described below, but the present invention is not limitedthereto.

As the method for obtaining an aromatic polymer, various methods usedfor aromatic polyamides may be used. For example, low temperaturesolution polymerization, interfacial polymerization, meltpolymerization, solid phase polymerization, vapor depositionpolymerization, and the like may be used. In the low temperaturesolution polymerization, that is to say, when an aromatic polymer isobtained from an acid dichloride and a diamine, it is desirable toconduct the polymerization in an aprotic organic polar solvent. In apolymer solution, when an acid dichloride and a diamine are used asmonomers, hydrogen chloride is formed as a byproduct. In the case ofneutralizing this, an inorganic neutralizer such as calcium hydroxide,calcium carbonate and lithium carbonate or an organic neutralizer suchas ethylene oxide, propylene oxide, ammonia, triethylamine,triethanolamine and diethanolamine is used. The reaction between anisocyanate and a carboxylic acid is carried out in the presence of acatalyst in an aprotic organic polar solvent.

When the polymerization is carried out using two or more kinds ofdiamines, available are a stepwise reaction method comprising addingdiamines one after another, adding an acid dichloride in an amount of 10to 99 mole % with respect to the diamines to react them, subsequentlyadding other diamines and further adding an acid dichloride to reactthem, and a method comprising adding all diamines after mixing themtogether, followed by adding acid dichloride to react them. Also in thecase of utilizing two or more kinds of acid chlorides, a stepwisemethod, a method of simultaneously adding, etc. may be used. In bothcases, the molar ratio of the whole diamines and the whole aciddichloride is preferably within the range of 95:105 to 105:95. If theratio is out of this range, it may be difficult to obtain a polymersolution suitable for shaping.

The “dissolution” referred to in the present invention means that astate where a polymer maintaining its fluidity without formingsuspension or gel is dispersed in a solvent persists for 24 hours ormore. In the polymer dissolution step, heat stirring may be conducted attemperatures equal to or lower than 100° C.

The polymer solution may be used as received as a stock solution for thepreparation of shaped articles. Alternatively, it is also permissive toisolate a polymer once and then redissolve it in the aforementionedorganic solvent or in an inorganic solvent such as sulfuric acid toprepare a stock solution.

The intrinsic viscosity of the polymer (the value of 100 ml of asolution with 0.5 g of the polymer dissolved in sulfuric acid, measuredat 30° C.) is preferably 0.5 or more.

To the polymer stock solution for obtaining shaped articles, aninorganic salt, e.g. calcium chloride, magnesium chloride, lithiumchloride, lithium nitrate and lithium bromide, may be added as adissolution aid. Halogen salts of Group 1 (alkali metals) or Group 2(alkaline earth metals) are preferred as the inorganic salt. Lithiumhalides such as lithium bromide and lithium chloride are morepreferable. Although the aromatic polymer of the present invention issoluble in organic solvent, dicarbohydrazide which is a source materialof the polymer is almost insoluble in organic solvent and a resultingpolymer also exerts a low solubility. It, therefore, is desirable to adda dissolution aid. The amount of the dissolution aid added is preferablyfrom 1 to 50% by weight with respect to the polymer. If it is 1% orless, the effect of the dissolution aid may hardly be shown. On theother hand, if the amount is more than 50%, some problems may arise,e.g. corrosion of a film-forming support during production of films.

The polymer concentration in a stock solution is preferably from 2 to40% by weight, more preferably from 5 to 35% by weight, and particularlypreferably from 10 to 25% by weight. If the polymer concentration isless than 2% by weight, a large amount of discharge is needed, resultingin economical disadvantages. If it exceeds 40% by weight, it may becomedifficult to obtain thin fibrous articles or thin film-like articles dueto the discharge amount or the solution viscosity.

Oligomers (low molecular weight substances) in the polymer solution maydeteriorate mechanical characteristics or thermal characteristics ofresulting shaped articles or qualities of products during theirapplication. Therefore, the amount of oligomers with molecular weightsof 1,000 or less is preferably 1% by weight or less of the polymer. Theamount of oligomers is more preferably 0.5% by weight or less. Theweight fraction of oligomers can be calculated by incorporating a lowangle laser light scattering spectrometer (LALLS) and a differentialrefractometer (RI) into a gel permeation chromatograph (GPC), measuringa light scattering intensity and a refractive index difference ofmolecular chain solutions which have been size-fractionated by means ofa GPC device with elution time, thereby calculating the molecularweights of solutes and their contents one after another, and finallydetermining the absolute molecular weight distribution of high molecularweight substances. Diphenylmethane is used for calibration of absolutemolecular weights.

In the production of the aromatic polymer of the present invention,examples of the aprotic polar solvent to be used include sulfoxidesolvents such as dimethylsulfoxide and diethylsulfoxide, formamidesolvents such as N,N-dimethylformamide and N,N-diethylformamide,acetamide solvents such as N,N-dimethylacetamide andN,N-diethylacetamide, pyrrolidone solvents such asN-methyl-2-pyrrolidone and N-vinyl-2-pyrrolidone, phenolic solvents suchas phenol, o-, m- or p-creosol, xylenol, halogenated phenols andcatechol, or hexamethylphosphoramide and γ-butyrolactone. These can beused solely or in the form of a mixture. Moreover, aromatic hydrocarbonssuch as xylene and toluene may also be used. Furthermore, for thepurpose of facilitating the dissolution of a polymer, it is alsopermissive to add, to the polymer, a salt of alkali metal or alkalineearth metal in an amount of 50% by weight or less with respect to thepolymer.

It is permissive to allow the aromatic polymer of the present inventionto contain 10% by weight or less of inorganic or organic additives forthe purpose of surface formation or processability improvement. Examplesof additives for surface formation include inorganic particles such asSiO₂, TiO₂, Al₂O₃, CaSO₄, BaSO₄, CaCO₃, carbon black, carbon nanotube,fullerene, zeolite and other metal fine powders. Preferable organicparticles include, for example, particles composed of organicmacromolecules such as crosslinked polyvinylbenzene, crosslinkedacrylics, crosslinked polystyrene, polyester particles, polyimideparticles, polyamide particles and fluororesin particles, or inorganicparticles applied with treatment to their surfaces such as coating withthe aforementioned organic macromolecules.

Next, the production of films is described. Because the aromatic polymerof the present invention is soluble in organic solvent, it does notnecessarily need a special film forming method using concentratedsulfuric acid as PPTA does. The film-forming stock solution prepared asdescribed above is subjected to the so-called solution casting processsimilarly to aromatic polyamide so as to form a film. The solutioncasting process includes a dry-wet process, a dry process and a wetprocess. Although films may be produced by any of those processes, thedry-wet process will now be described as an example.

When the film is prepared by a dry-wet process, the film-formingsolution is extruded through a die onto a support such as a drum or anendless belt to form a thin film. The thin film layer is then dried byevaporation of the solvent until the thin film acquires self-supportingproperty. The drying may be carried out at room temperature to 220° C.for not more than 60 minutes. When the drum or endless belt used in thedrying step is as smooth as possible, it is possible to obtain a filmwith a smooth surface. The film after the above-mentioned dry process ispeeled off from the support and subjected to a wet process in whichdesalting and desolventing are conducted. In addition, it is stretched,dried and heat treated to yield a film.

Regarding the stretching, the stretching ratio in area stretching ratiois preferably within the range of from 0.8 to 8, more preferably from1.3 to 8. The area stretching ratio is defined as a value obtained bydividing the area of the film after stretching by the area of the filmbefore stretching. The area stretching ratio not more than 1 means beingrelaxed. Regarding the heat treatment, it is conducted at a temperatureof 200° C. to 500° C., preferably 250° C. to 400° C. for several secondsor several minutes. It is effective to slowly cool the film after thestretching or the heat treatment. It is effective to cool the film at arate of not more than 50° C./second.

After being shaped into film, the aromatic polymer film of the presentinvention may also be stretched again under conditions of 300° C. orhigher. The high temperature stretching step of the film of the presentinvention is preferably conducted within a temperature range of 300 to600° C., more preferably 350 to 550° C. The high temperature stretchingmay be conducted in a medium inert to the polymer, e.g. in the air, innitrogen, in argon, in carbon dioxide gas and in helium. Because thepolymer film inherently has a high glass transition temperature (250° C.or higher), the film may chaps at low temperature stretching and,therefore, may rupture at a low stretching ratio.

Next, dehydration-cyclization is described. Using the stock solutionobtained in the above-mentioned method, namely, the solution of anaromatic amide carbohydrazide in organic solvent, the operations shownbelow as examples are carried out. (1) To extrude the solution through adie onto a support such as a drum or an endless belt to form a thin filmand then immerse the film in a dehydration-cyclization agent solutionbath. (2) To add a dehydration-cyclization agent solution to a stocksolution just before a die and then extrude the resulting solutionthrough the die onto a support such as a drum or a endless belt and coolit to form a thin film. Or, (3) To extrude a stock solution through adie onto a support such as a drum or an endless belt to form a thinfilm, and then dry it by evaporation of the solvent from the thin filmlayer until the thin film acquires self-supporting property. Theself-supporting film is peeled off from the support and then immersed ina dehydration-cyclization agent solution bath. Although theabove-mentioned methods are shown as examples, the method of cyclizingby dehydration is not restricted thereto. The film cyclized bydehydration is further stretched, dried and heat treated to yield afilm. Heat treatment conditions are at a temperature of 200° C. to 500°C., preferably 250° C. to 400° C. for several seconds or severalminutes.

The film of the present invention may be either a monolayer film or amultilayer film. The film of the present invention is used suitably forvarious applications such as flexible printed circuit substrates,semiconductor-mounting substrates, multilayer circuit substrates,capacitors, printer ribbons, sound diaphragms, base films of solarbatteries and electrolyte membranes. The film of the present inventionis particularly preferably used as a magnetic recording medium in whicha magnetic layer has been formed on at least one side because effects ofthe film of the present invention having both a high power and a highdurability are fully exerted.

The film of the present invention can be used as an acid-base typehydrocarbon polymer electrolyte membrane when being doped with acid suchas sulfuric acid and phosphoric acid to form an aromatic polymer/acidcomposite. In addition, the film of the present invention can be used asan electrolyte membrane when the aromatic polymer is modified with apolar group. Here, examples of the polar group include a sulfonic acidgroup, a sulfuric acid group, a phosphonic acid group, a phosphoric acidgroup and a carboxylic acid group. The method for the modificationinclude a method of modifying by immersing the aromatic polymer film ofthe present invention in a solution of concentrated sulfuric acid,chlorosulfuric acid, fuming sulfuric acid, sulfonic acid and phosphonicacid (method 1) and a method using a raw material having a substituentas a raw material when polymerizing the aromatic polymer of the presentinvention (method 2).

Next, the method for producing the polymer electrolyte membrane of thepresent invention is described in more detail on the basis of theabove-mentioned method 1.

In the polymer electrolyte film of the present invention, it isimportant that a polar group exists at least in a void in the membrane.The polar group may be selected appropriately depending on the ion toconduct and may be either an anionic group or a cationic group. Forexample, in the case of using the membrane as a proton conductingmembrane of a fuel cell or the like, preferred is an anionic group, suchas a sulfonic acid group, a sulfuric acid group, a phosphonic acidgroup, a phosphoric acid group and a carboxylic acid group.

Explanation is made by taking, as an example, a case of introducing ananionic group by a polymer reaction. Introduction of a phosphonic acidgroup to an aromatic polymer can be achieved by, for example, a methoddisclosed in Polymer Preprints, Japan, 51, 750 (2002). Introduction of aphosphoric acid group to an aromatic polymer can be achieved by, forexample, phosphate esterification of an aromatic polymer having ahydroxyl group. Introduction of a carboxylic acid group to an aromaticpolymer can be achieved by, for example, oxidizing an aromatic polymerhaving an alkyl group, a hydroxyalkyl group, or the like. Introductionof a sulfuric acid group to an aromatic polymer can be achieved by, forexample, sulfate esterification of an aromatic polymer having a hydroxylgroup. As a method for sulfonating an aromatic polymer, namely a methodfor introducing a sulfonic acid group, methods disclosed in JapanesePatent Application Publication No. 2-16126 or Japanese PatentApplication Publication No. 2-208322 are known, for example. Concretely,for example, sulfonation can be achieved by allowing an aromatic polymerto react with a sulfonation agent such as chlorosulfonic acid in solventor by allowing them to react in concentrated sulfuric acid or fumingsulfuric acid. Available as the solvent is a solvent which does notreact with a polar group-introducing agent or which does not react veryviolently and can permeate the polymer. Examples of such a solventinclude halogenated hydrocarbons such as chloroform, 1,2-dichloroethane,dichloromethane and perchloroethylene, nitrated hydrocarbons such asnitromethane and nitroethane, and nitrites such as acetonitrile. Thesolvent and the polar group-introducing agent each may be either asingle substance or a mixture of two or more kinds.

The sulfonating agent is not particularly restricted if it is one whichcan sulfonate an aromatic polymer. Besides those mentioned above, sulfurtrioxide and the like can be employed. When sulfonating an aromaticpolymer by this method, it is possible to control the degree ofsulfonation easily by the amount of the sulfonating agent used, thereaction temperature and the reaction time. Introduction of asulfonimide group to an aromatic polymer can be achieved by, forexample, a method of allowing a sulfonic acid group and a sulfonamidegroup to react.

When using as an electrolyte membrane, it is believed that a H⁺ ion,namely, a proton moves together with a water molecule. It is desirablethat the membrane have a moisture absorption of several percent toseveral tens percent.

For manufacturing a high-power polymer electrolyte type fuel cell with ahigh energy capacity, it is desirable that the ion conductance and thefuel permeation amount be within the ranges described below.

With a polymer electrolyte membrane processed into a film having athickness ranging from 10 μm to 500 μm, the ionic conductance in wateris preferably 10 mS/cm or more. When less than 10 mS/cm, it is hard toobtain a high power as a battery. The ionic conductance is preferably 40mS/cm or more, and more preferably 60 mS/cm or more. Although no upperlimit is particularly set, the greater the ionic conductance, the betterit is unless the film dissolves or disintegrates by the action of thefuel. The ionic conductance referred to herein can be determined byimmersing a sample in pure water at 25° C. for 24 hours, followed byremoving it to an atmosphere at 25° C. and a relative humidity of 50 to80% and measuring a resistance by the controlled-potential AC impedancemethod.

The electrolyte membrane of the present invention is widely used forapplications such as fuel cells, production of table salt, production ofdrinking water or industrial water, desalting purification of chemicalagents, treatment of dairy products, production of low-salt soy sauce,recovery or purification of metal or free acid, production of hydrogenand oxygen by electrolysis of water, and production of acid or alkali byelectrolysis of salt. The electrolyte membrane of the present inventionis particularly useful as an electrolyte membrane for fuel cell. Moreparticularly, it can be utilized suitably for solid polymer type fuelcells, direct methanol type solid polymer fuel cells and phosphoric acidtype fuel cells.

The film of the present invention is also applicable as a partition ofelectrolytic solution, namely, a separator due to its high heatresistance and mechanical strength. In this case, it is desirable to usethe film of the present invention after rendering it porous.

A schematic diagram of a solid polymer type fuel cell is shown inFIG. 1. On a surface of an electrolyte membrane 1, a catalyst usingplatinum or the like (not shown) has been applied. On both sides of theelectrolyte membrane 1, two electrodes, a fuel electrode 2 and an airelectrode 3, are disposed. As materials of the electrodes, carbonmaterial or the like is suitably used. Separators 4 are disposed outsidethe electrodes. Although not shown in the diagram, a gas passage isformed between each electrode and each separator. When fuel gas 5 suchas hydrogen is supplied to the passage of the side of the fuel electrode2 and gas 6 containing oxygen, such as air, is supplied to the passageof the side of the air electrode 3, an electrochemical reaction takesplace on the catalyst and, as a result, an electric current is produced.

There is not particular limitations with applications of the fuel cell,it can be used suitably for electronic devices, electric devices, homepower source, commercial power generation, aerospace applications andtransportation.

The present invention will be explained in more detail with reference tothe following Examples.

The methods for measuring physical properties and evaluating effects inthe present invention are described below.

(1) Young's Modulus, Strength and Elongation at Break

A film was sampled and was measured at a specimen width of 10 mm, aspecimen length of 50 mm, a tensile speed of 300 mm/min, 23° C. and 65%RH using a Robot Tensilon RTA-100 (manufactured by ORIENTEC Co., Ltd.).In the specimen, the direction of film formation (MD) was defined as thewidth direction and a direction perpendicular thereto was defined as thelength direction.

(2) Moisture Absorption Rate

About 0.5 g of film was taken and heated at 120° C. for 3 hours fordemoisturing. Then, the temperature was lowered to 25° C. while the filmwas prevented from moisture absorption. The weight after the temperaturelowering was measured accurately to the order of 0.1 mg, where theweight was represented by W₀. Subsequently, it was left to stand in anatmosphere at 25° C., 75 RH % for 48 hours. Then, the weight wasmeasured, which was represented by W₁. The moisture absorption wascalculated by use of the following equation.

Moisture absorption rate (%)=((W ₁ −W ₀)/W ₀)×100

(3) Solubility of Polymer

A polymer whose solution after the completion of polymerization wasimpossible to be processed into film due to gelation was judged as x. Apolymer whose solution after the completion of polymerization waspossible to be processed into film in spite of gelation or loss oftransparency was judged as A. A polymer whose solution after thecompletion of polymerization and after being left to stand at 23° C. for24 hours was transparent and was possible to be processed into film wasjudged as o.

(4) Method for Determining Conductivity

Regarding the ionic conductance, a sample was immersed in pure water at25° C. for 24 hours, then removed to an atmosphere at 25° C. and arelative humidity of 50 to 80%, and measured for a resistance by thecontrolled-potential AC impedance method described below.

Using an electrochemical analysis system (Solartron 1287 ElectrochemicalInterface and Solartron 1255B Frequency Response Analyzer) manufacturedby Solartron, a sample was sandwiched between two round electrodes (madeof stainless steel), one having a diameter of 2 mm and the other havinga diameter of 10 mm, under a load of 1 kg (effective electrode area:0.0314 cm²). To the interfaces between the sample and the electrodes, a15% aqueous solution of poly(2-acrylamide-2-methylpropanesulfonic acid)was applied. The ionic conductance in the film thickness direction wasdetermined through measurement of the controlled-potential impedance at25° C. (AC amplitude: 50 mV).

(5) Glass Transition Temperature (Tg):Dynamic ViscoelasticityMeasurement

Apparatus: DMS6100 viscoelasticity spectrometer (manufactured by SeikoInstruments Inc.)

According to ASTM E1640-94, an inflection point of E′ was designated asTg. Because of the limit with the apparatus, it was impossible todetermine glass transition temperatures higher than 360° C., which were,therefore, recorded as “360° C. or higher”.

Example 1

A 200-ml, four-necked flask equipped with a stirrer was charged with3.6638 g of 2,6-naphthalene dicarbohydrazide, 4.3850 g of1,3-bis-(4-aminophenoxy)benzene, 149.67 ml of N-methyl-2-pyrrolidone and5.98 g of lithium bromide, followed by stirring under nitrogen under icecooling. During a period from 10 to 30 minutes later, 6.091 g ofterephthaloyl dichloride was added in five portions. After stirring foradditional one hour, hydrogen chloride produced during the reaction wasneutralized with 2.139 g of lithium carbonate to yield a transparentpolymer solution. Even after being left to stand for two weeks, thepolymer solution was transparent and maintained its fluidity.

A portion of the resulting polymer solution was taken on a glass plateand then a uniform film was formed therefrom with a bar coater. The filmwas heated at 120° C. for seven minutes to yield a self-supporting film.The resulting film was removed from the glass plate and was fixed in ametal frame. It was washed with running water for 10 minutes and thensubjected to heat treatment at 280° C. for one minute to yield anaromatic polymer film. The Young's modulus and moisture absorption ofthe resulting film were measured, which are shown in Table 1. The glasstransition temperature detected in the dynamic viscoelasticitymeasurement was 360° C. or higher.

Example 2

A 200-ml, four-necked flask equipped with a stirrer was charged with1.4655 g of 2,6-naphthalene dicarbohydrazide, 4.0926 g of1,3-bis-(4-aminophenoxy)benzene, 68.31 ml of N-methyl-2-pyrrolidone and4.08 g of lithium bromide, followed by stirring under nitrogen under icecooling. During a period from 10 to 30 minutes later, 4.0604 g ofterephthaloyl dichloride was added in five portions. After stirring foradditional one hour, hydrogen chloride produced during the reaction wasneutralized with 1.426 g of lithium carbonate to yield a transparentpolymer solution. Even after being left to stand for two weeks, thepolymer solution was transparent and maintained its fluidity.

A portion of the resulting polymer solution was taken on a glass plateand then a uniform film was formed therefrom with a bar coater. The filmwas heated at 120° C. for seven minutes to yield a self-supporting film.The resulting film was removed from the glass plate and was fixed in ametal frame. It was washed with running water for 10 minutes and thensubjected to heat treatment at 280° C. for one minute to yield anaromatic polymer film. The Young's modulus and moisture absorption ofthe resulting film were measured, which are shown in Table 1.

Example 3

A 200-ml, four-necked flask equipped with a stirrer was charged with2.931 g of 2,6-naphthalene dicarbohydrazide, 1.2977 g ofparaphenylenediamine, 1.2014 g of 4,4′-diaminodiphenyl ether, 115.89 mlof N-methyl-2-pyrrolidone and 4.67 g of lithium bromide, followed bystirring under nitrogen under ice cooling. During a period from 10 to 30minutes later, 6.0906 g of terephthaloyl dichloride was added in fiveportions. After stirring for additional one hour, hydrogen chlorideproduced during the reaction was neutralized with 2.1391 g of lithiumcarbonate to yield a transparent polymer solution. Even after being leftto stand for two weeks, the polymer solution was transparent andmaintained its fluidity.

A portion of the resulting polymer solution was taken on a glass plateand then a uniform film was formed therefrom with a bar coater. The filmwas heated at 12⁰° C. for seven minutes to yield a self-supporting film.The resulting film was removed from the glass plate and was fixed in ametal frame. It was washed with running water for 10 minutes and thensubjected to heat treatment at 280° C. for one minute to yield anaromatic polymer film. The Young's modulus and moisture absorption ofthe resulting film were measured, which are shown in Table 1.

Example 4

A 200-ml, four-necked flask equipped with a stirrer was charged with2.4425 g of 2,6-naphthalene dicarbohydrazide, 4.3250 g ofbis[4-(4-aminophenoxy)phenyl]sulfone, 78.88 ml of N-methyl-2-pyrrolidoneand 4.68 g of lithium bromide, followed by stirring under nitrogen underice cooling. During a period from 10 to 30 minutes later, 4.0604 g ofterephthaloyl dichloride was added in five portions. After stirring foradditional one hour, hydrogen chloride produced during the reaction wasneutralized with 1.426 g of lithium carbonate to yield a transparentpolymer solution. Even after being left to stand for two weeks, thepolymer solution was transparent and maintained its fluidity.

A portion of the resulting polymer solution was taken on a glass plateand then a uniform film was formed therefrom with a bar coater. The filmwas heated at 120° C. for seven minutes to yield a self-supporting film.The resulting film was removed from the glass plate and was fixed in ametal frame. It was washed with running water for 10 minutes and thensubjected to heat treatment at 280° C. for one minute to yield anaromatic polymer film. The Young's modulus and moisture absorption ofthe resulting film were measured, which are shown in Table 1.

Example 5

A portion of the polymer solution of Example 4 was taken on a glassplate and then a uniform film was formed therefrom with a bar coater.This is immersed in a bath composed of 50% by weight of diethanolamineand 50% by weight of NMP for five minutes to yield a self-supportingfilm. The resulting film was washed with running water for 10 minutesand then subjected to heat treatment at 280° C. for one minute to yieldan aromatic polymer film. The Young's modulus of the resulting film wasmeasured, which is shown in Table 1.

Example 6

A 200-ml, four-necked flask equipped with a stirrer was charged with8.5488 g of 2,6-naphthalene dicarbohydrazide, 3.0036 g of4,4′-diaminodiphenyl ether, 150.30 ml of N-methyl-2-pyrrolidone and 9.03g of lithium bromide, followed by stirring under nitrogen under icecooling. During a period from 10 to 30 minutes later, 10.1510 g ofterephthaloyl dichloride was added in five portions. After stirring foradditional one hour, hydrogen chloride produced during the reaction wasneutralized with 3.5652 g of lithium carbonate to yield a transparentpolymer solution. Even after being left to stand for two weeks, thepolymer solution was transparent and maintained its fluidity.

A portion of the resulting polymer solution was taken on a glass plateand then a uniform film was formed therefrom with a bar coater. The filmwas heated at 120° C. for seven minutes to yield a self-supporting film.The resulting film was removed from the glass plate and was fixed in ametal frame. It was washed with running water for 10 minutes and thensubjected to heat treatment at 280° C. for one minute to yield anaromatic polymer film. The Young's modulus and moisture absorption ofthe resulting film were measured, which are shown in Table 1.

Example 7

A portion of the polymer solution of Example 6 was taken on a glassplate and then a uniform film was formed therefrom with a bar coater.This is immersed in a bath composed of 50% by weight of diethanolamineand 50% by weight of NMP for five minutes to yield a self-supportingfilm. The resulting film was washed with running water for 10 minutesand then subjected to heat treatment at 300° C. for five minutes toyield an aromatic polymer film. The Young's modulus of the resultingfilm was measured, which is shown in Table 1.

Example 8

A 200-ml, four-necked flask equipped with a stirrer was charged with13.43 g of 2,6-naphthalene dicarbohydrazide, 188.78 ml ofN-methyl-2-pyrrolidone and 9 g of lithium bromide, followed by stirringunder nitrogen under ice cooling. During a period from 10 to 30 minuteslater, 13.06 g of 2-chloro-1,4-phthaloyl dichloride was added in fiveportions. After stirring for additional one hour, hydrogen chlorideproduced during the reaction was neutralized with 3.92 g of lithiumcarbonate to yield a transparent polymer solution. Even after being leftto stand for two weeks, the polymer solution was transparent andmaintained its fluidity.

A portion of the resulting polymer solution was taken on a glass plateand then a uniform film was formed therefrom with a bar coater. The filmwas heated at 120° C. for seven minutes to yield a self-supporting film.The resulting film was removed from the glass plate and was fixed in ametal frame. It was washed with running water for 10 minutes and thensubjected to heat treatment at 280° C. for one minute to yield anaromatic polymer film.

Example 9

A portion of the polymer solution of Example 8 was taken on a glassplate and then a uniform film was formed therefrom with a bar coater.This is immersed in a bath composed of 50% by weight of diethanolamineand 50% by weight of NMP for five minutes to yield a self-supportingfilm. The resulting film was washed with running water for 10 minutesand then subjected to heat treatment at 300° C. for five minutes toyield an aromatic polymer film.

Example 10

A 200-ml, four-necked flask equipped with a stirrer was charged with6.11 g of 2,6-naphthalene dicarbohydrazide, 8.71 g of9,9-bis(4-aminophenyl)fluorene, 179 ml of N-methyl-2-pyrrolidone and 9 gof lithium bromide, followed by stirring under nitrogen under icecooling. During a period from 10 to 30 minutes later, 10.16 g ofterephthaloyl dichloride was added in five portions. After stirring foradditional one hour, hydrogen chloride produced during the reaction wasneutralized with 3.57 g of lithium carbonate to yield a transparentpolymer solution. Even after being left to stand for two weeks, thepolymer solution was transparent and maintained its fluidity.

A portion of the resulting polymer solution was taken on a glass plateand then a uniform film was formed therefrom with a bar coater. The filmwas heated at 120° C. for seven minutes to yield a self-supporting film.The resulting film was removed from the glass plate and was fixed in ametal frame. It was washed with running water for 10 minutes and thensubjected to heat treatment at 280° C. for one minute to yield anaromatic polymer film.

Example 11

The polymer film obtained in Example 5 was immersed in1,2-dichloroethane containing 3% by weight of chlorosulfonic acid at 25°C. for 15 minutes and then removed. The film was washed with methanol toremove 1,2-dichloroethane and then was washed with water until thewashings became neutral. Thus, a 72-μm thick polymer electrolytemembrane was produced. The resulting polymer electrolyte membrane had aresistance of 34 Ω and an ionic conductance of 6.8 mS/cm.

Example 12

The polymer film obtained in Example 7 was immersed in1,2-dichloroethane containing 3% by weight of chlorosulfonic acid at 25°C. for 15 minutes and then removed. The film was washed with methanol toremove 1,2-dichloroethane and then was washed with water until thewashings became neutral. Thus, a 41-μm thick polymer electrolytemembrane was produced. The resulting polymer electrolyte membrane had aresistance of 5 Ω and an ionic conductance of 6.8 mS/cm.

Comparative Example 1

A 200-ml, four-necked flask equipped with a stirrer was charged with12.0 g of paraphenylene terephthalamide, 6.0 g of lithium bromide and108 ml of N-methyl-2-pyrrolidone, followed by stirring under nitrogen at60° C. The paraphenylene terephthalamide did not dissolve even after alapse of 48 hours and, therefore, it was impossible to form a film.

Comparative Example 2

A 200-ml, four-necked flask equipped with a stirrer was charged with1.622 g of 1,4-phenylenediamine,. 3.0036 g of 4,4′-diaminodiphenyl etherand 70.3 ml of N-methyl-2-pyrrolidone, followed by stirring undernitrogen under ice cooling. During a period from 10 to 30 minutes later,6.091 g of terephthaloyl dichloride was added in five portions. Afterstirring for additional one hour, hydrogen chloride produced during thereaction was neutralized with 2.139 g of lithium carbonate to yield atransparent polymer solution. After being left to stand for 12 hours,the polymer solution was gelated to fall into a state where it could notbe formed into film.

Comparative Example 3

A 200-ml, four-necked flask equipped with a stirrer was charged with4.9664 g of 4,4′-diaminodiphenylsulfone and 63.14 ml ofN-methyl-2-pyrrolidone, followed by stirring under nitrogen under icecooling. During a period from 10 to 30 minutes later, 4.0604 g ofterephthaloyl dichloride was added in five portions. After stirring foradditional one hour, hydrogen chloride produced during the reaction wasneutralized with 1.426 g of lithium carbonate to yield a transparentpolymer solution.

A portion of the resulting polymer solution was taken on a glass plateand then a uniform film was formed therefrom with a bar coater. The filmwas heated at 120° C. for seven minutes to yield a self-supporting film.The resulting film was removed from the glass plate and was fixed in ametal frame. It was washed with running water for 10 minutes and thensubjected to heat treatment at 280° C. for one minute to yield anaromatic polymer film. The Young's modulus and moisture absorption ofthe resulting film were measured, which are shown in Table 1.

TABLE 1 Solubility Moisture Coefficient of Young's Elongation absorptionof moisture Dehydration- source modulus at rate expansion l + m + n l mn cyclization polymer (GPa) break (%) (%) (ppm/% Rh) Example 1 100 0 5050 No ∘ 7.7 29.9 3.5 35 Example 2 100 0 70 30 No ∘ 5.6 17.9 3.5 Example3 100 40 20 40 No ∘ 8.9 33.5 6.7 Example 4 100 0 50 50 No ∘ 5.4 42.5 5.6Example 5 100 0 50 50 Yes ∘ 7.7 9.1 5.9 Example 6 100 0 30 70 No ∘ 9.811.7 5.2 Example 7 100 0 30 70 Yes ∘ 14.8 1.7 8.0 Example 8 100 0 0 100No ∘ Example 9 100 0 0 100 Yes ∘ Example 10 100 0 50 50 No ∘ Comparative100 100 0 0 No x Impossible Impossible Impossible Example 1 to to toform a form a form a film film film Comparative 100 50 50 0 No xImpossible Impossible Impossible Example 2 to to to form a form a form afilm film film Comparative 100 100 0 No ∘ 3.6 50 6.8 189 Example 3

INDUSTRIAL APPLICABILITY

According to the present invention, obtained were an aromaticcarbohydrazide and a resulting aromatic polymer fromdehydration-cyclization of such an aromatic carbohydrazide, which aresoluble in an aprotic polar solvent and which exhibit a high Young'smodulus, a great elongation at break and a low moisture absorption whenbeing formed into a film. The aromatic polymer of the present inventionis conformable to a current trend that halogen-containing polymers arenot preferred because it has excellent characteristics even though itcontains no halogen atoms.

Films containing the aromatic polymer of the present invention are usedsuitably for various applications such as magnetic recording medium,flexible printed circuit substrates, semiconductor-mounting substrates,multilayer circuit substrates, capacitors, printer ribbons, sounddiaphragms, base films of solar batteries and electrolyte membranes. Useof the film as a magnetic recording medium is particularly preferablebecause the effects of the present invention will be fully shown.

Film containing the aromatic polymer of the present invention can beused as an acid-base type hydrocarbon polymer electrolyte membrane whenbeing doped with an acid to form an aromatic polymer/acid composite. Inaddition, films containing the aromatic polymer of the present inventioncan be used as an electrolyte membrane when the aromatic polymer ismodified with a polar group. The electrolyte membrane of the presentinvention is particularly useful as an electrolyte membrane for fuelcells.

In addition, according to the method of the present invention, acarbohydrazide structure was caused to react successfully under mildconditions at low cost.

1. A method for producing a film which comprises an aromatic amideoxadiazole polymer containing an oxadiazole structure, the methodcomprising: immersing a film containing a carbohydrazide structure in adehydration-cyclization agent solution bath, wherein thedehydration-cyclization agent is a base; and heat treating the film at atemperature of 200° C. to 500° C. for several seconds to severalminutes.
 2. The method according to claim 1, wherein the base is anitrogen-containing compound having 0 to 10 carbon atoms.
 3. A filmcomprising an aromatic amide oxadiazole polymer containing an oxadiazolestructure and which is obtained by immersing a film containing acarbohydrazide structure in a dehydration-cyclization agent solutionbath, wherein the dehydration-cyclization agent is a base; and heattreating the film at a temperature of 200° C. to 500° C. for severalseconds to several minutes